Chapter 10 Wireless Communications

1. Chapter 10Wireless Communications Information Technology in Theory By Pelin Aksoy and Laura DeNardis

2. Objectives • Understand the various applications that use radio waves • Learn about satellite components and satellite orbits • Understand the effects of the atmosphere on radio waves Information Technology in Theory

3. Objectives (continued) • Learn about the underlying principles of the global positioning system • Gain exposure to satellite-based Internet services and radio frequency identification Information Technology in Theory

4. Applications of Radio Frequency • Ever since Guglielmo Marconi first demonstrated how to communicate using long-distance radio waves, people have used them for information exchange • The frequency of radio waves ranges from a few hertz to hundreds of billions of hertz • Most of our daily activities involve some form of wireless communication, such as listening to the radio or talking on a cellular phone Information Technology in Theory

5. Applications of Radio Frequency (continued) Information Technology in Theory

6. Digital Radio and TV Broadcasting • The traditional AM and FM techniques are still used extensively for radio broadcasting • Analog radio is vulnerable to unwanted effects such as interference from other sources, which cannot be removed effectively • Digital radio, which uses effective error-control techniques, was developed as a higher-quality alternative for radio listeners Information Technology in Theory

7. Digital Radio and TV Broadcasting (continued) • Such services, which use digital signals to transmit information, are also called digital audio broadcasting (DAB) and high-definition radio (HD radio) • These technologies offer high-fidelity music that is close to CD quality, as well as digital broadcasting that enables receivers to display moving pictures, other multimedia, and text Information Technology in Theory

8. Digital Radio and TV Broadcasting (continued) • Because terrestrial radio broadcasting has a limited reach, satellite radio has become an attractive alternative • Satellite television providers broadcast signals via satellite to customers over a large area • Digital television (DTV) broadcasting enables the transmission of many high-quality channels, high-fidelity audio, and such features as pay-per-view and video on demand Information Technology in Theory

9. Digital Radio and TV Broadcasting (continued) • Many cable companies provide digital broadcast services to consumers in the form of digital cable • High-definition television (HDTV) is also in demand for its superior picture and sound quality Information Technology in Theory

10. National Defense and Emergency Services • Military ships, aircraft, and terrestrial units are in constant communication via designated radio frequencies • One major difference between civilian and military communications is the level of security • Another critical application of radio waves is in emergency dispatch services Information Technology in Theory

11. Aviation and Maritime Communication • Private jets, commercial airliners, and military planes all use radio waves to communicate with airports and other ground stations en route to their destinations • Numerous maritime satellite systems such as Inmarsat (International Maritime Satellite Organization) are specifically designed to provide maritime communications Information Technology in Theory

12. Computer Networks • One popular wireless networking technology is wireless fidelity (Wi-Fi), which uses radio waves at frequencies of 2.4 GHz and 5 GHz • Another important wireless networking standard, Bluetooth, is used to connect mouses, keyboards, printers, and digital cameras to computers Information Technology in Theory

13. Computer Networks (continued) • Another significant wireless technology that has gained attention is WiMAX • WiMAX is considered an alternative to DSL and cable modems for providing metropolitan wireless connectivity between users and Internet service providers Information Technology in Theory

14. The Telephone Network • Radio waves in telephony applications are most often encountered in the following areas: • Between a cordless telephone and its base station • Between a wireless headset and a mobile telephone • Within the telephone network in areas that employ satellites • Within the telephone network in areas that use long-distance terrestrial microwave links • Between cellular telephones and base station antennas • Between a satellite phone and the satellite Information Technology in Theory

15. Navigation • The global positioning system (GPS) uses a combination of numerous satellites, receivers, and ground stations to give positional information in three dimensions Information Technology in Theory

16. Space Exploration • Because electromagnetic waves can travel through a vacuum, they are used in deep space exploration Information Technology in Theory

17. Remote Sensing • One of the most common remote sensing techniques is RADAR • RADAR works by emitting radio waves toward an object and analyzing the reflections of the waves from it • These results can then be used to take speed and distance measurements Information Technology in Theory

18. Radio Frequency Identification (RFID) • An RFID system is made up of small RFID tags that emit radio frequencies and readers that can detect and read the information stored on the tags • RFID is an innovative approach for identifying and tracking shipping containers, pets, and sometimes even people • RFID tags are classified as either active or passive Information Technology in Theory

19. Personal and Commercial • Many personal applications rely on radio waves, including baby monitors, remote keyless entry features on cars, microwave ovens, and garage door openers • Others include amateur radio (i.e. ham radio) and citizens band radio • VSATs enable businesses to serve customers who want to make purchases with their credit cards Information Technology in Theory

20. Satellite Systems • Beginning with the launch of Sputnik in 1957, the space race between the former Soviet Union and the United States spurred rapid advances in satellite technology and significant developments in space travel and exploration • Hundreds of satellites currently orbit the Earth Information Technology in Theory

21. Satellite Components • Antennas • Solar panels • Communications payload • Control system Information Technology in Theory

22. Satellite Components (continued) Information Technology in Theory

23. Satellite Components (continued) Information Technology in Theory

24. Satellite Orbits • The altitude of the satellite usually classifies it into one of the following categories, although other categories exist: • Low Earth orbit (LEO) satellite • Medium Earth orbit (MEO) satellite • Geostationary Earth orbit (GEO) satellite Information Technology in Theory

25. Satellite Orbits (continued) Information Technology in Theory

26. Satellite Orbits (continued) Information Technology in Theory

27. Satellite Orbits (continued) Information Technology in Theory

28. Effects of the Atmospheric Channel on Radio Waves • Interference from other radio sources • Signal attenuation due to atmospheric effects, such as cloud cover, rain, ice • Reflections from buildings and other reflective surfaces • Not all radio wavelengths encounter the same effects in the atmosphere Information Technology in Theory

29. Effects of the Atmospheric Channel on Radio Waves (continued) • High-frequency radio waves that have short wavelengths are more susceptible to absorption and scattering, which arise due to water vapor and other atmospheric particles, than radio waves with low frequency and large wavelengths Information Technology in Theory

30. The Global Positioning System (GPS) • GPS is used to provide positional information in three-dimensional space (latitude, longitude, and elevation) through a GPS receiver and a network of satellites • Originally intended for military applications but is now also open for commercial use • The GPS is a network of about 24 MEO satellites and numerous Earth stations that constantly monitor these satellites Information Technology in Theory

31. The Global Positioning System (GPS) (continued) • The basis of GPS is called triangulation (sometimes also called trilateration) • Positional information can be obtained by means of triangulation, if the distance from at least three reference points is known Information Technology in Theory

32. The Global Positioning System (GPS) (continued) Information Technology in Theory

33. The Global Positioning System (GPS) (continued) • The distance from each satellite and the receiver is measured by generating a unique bit pattern for each satellite and synchronizing it with the GPS receiver • The next step is to use the positional information of the satellites to calculate the position of the receiver Information Technology in Theory

34. The Global Positioning System (GPS) (continued) • Because satellites have predetermined orbits, their exact location at particular times can be stored in the GPS receiver beforehand or periodically transmitted to the receiver • Using these two pieces of information, the receiver can calculate the latitude, longitude, and elevation of the aircraft with respect to the Earth Information Technology in Theory

35. The Global Positioning System (GPS) (continued) • Although many satellite measurements are necessary for accurate estimates, they still might not produce exact results because of other effects acting on the system • DGPS enables almost perfect calculations by including another measurement taken by designated Earth stations acting as satellites Information Technology in Theory

36. Satellite Internet • Broadband terrestrial Internet service is not available everywhere in the world • The setup for a satellite Internet connection is very simple: it requires a subscription to a satellite Internet service; a small receiving/transmitting terminal, such as a VSAT; and a satmodem, the modem used for communicating directly with the satellite Information Technology in Theory

37. Satellite Internet (continued) • The VSAT transmits and receives RF signals from the satellite, which then transponds the message to an Earth hub station that handles all the traffic in and out of the satellite • Two-way connection is typically asymmetrical, and downloads are generally faster than uploads Information Technology in Theory

38. Summary • Radio-wave communication provides mobility and flexibility in a wide range of applications, including radio and TV broadcasting, national defense and emergency services, aviation and maritime communications, computer and telephone networks, navigation, space exploration, remote sensing, radio frequency identification, and personal and commercial applications • Satellites receive radio frequency signals, process them, and relay them to their destination • A satellite’s major components include antennas, solar panels, a communications payload, and a control system Information Technology in Theory

39. Summary (continued) • Satellites may use a low Earth orbit (LEO), medium Earth orbit (MEO), or geostationary Earth orbit, among others • LEO satellites are closer to the surface of the Earth than MEOs and GEOs but have a smaller area of coverage; they complete a revolution of the Earth in much less time than MEOs and GEOs • GEOs revolve around the Earth in 24 hours, directly above the equator, which makes them appear stationary when seen from Earth Information Technology in Theory

40. Summary (continued) • The atmosphere has several detrimental effects on radio waves, including absorption and scattering • These effects attenuate the strength of the waves, limiting the extent to which they can travel and their maximum data rate • GPS is used for a variety of applications ranging from navigation to surveying Information Technology in Theory

41. Summary (continued) • The main principle of GPS is called triangulation, whereby multiple satellites are used to triangulate a position in three-dimensional space • Differential GPS is more accurate than regular GPS • Satellite Internet services are used primarily by customers who do not have access to a landline Internet connection, such as a cable modem or DSL Information Technology in Theory